Filter pin connectors provide an economical way to filter electromagnetic interference (EMI) and radio frequency interference (RFI) along signal paths between electronic equipment. For example, a low-pass filter may be built into each filter pin connector pin contact so that the filter pin connector passes D.C. and low-frequency AC signals while attenuating high frequencies. There are several types of filter pin connectors, each having a different circuit design depending on its intended use, e.g., L-type, L-C type, T-section, pi-section, etc., each named for their schematic diagram.
Long unshielded cable runs are particularly susceptible to interference, and therefore it may be necessary to provide electrical filters as an integral part of a connector in such a cable run to suppress EMI and RFI. Additionally, if the electronic equipment is intended for use in an environment contaminated with a high degree of EMI and RFI, e.g., electronic equipment used in aircraft, it may be necessary to provide filter pin connectors in the cable runs to allow proper operation of the equipment. In addition to protecting electronic equipment against EMI and RFI, filter pin connectors are used to protect equipment against electrical power surges that result from electrostatic discharges caused, for example, by a lightning strike. Filter pin connectors are particularly useful in telecommunications systems, data processing and microprocessor based systems, motor vehicles and aircraft.
Typically, only high potential voltage (Hipot) testing is conducted on filter pin connectors during manufacture. Hipot testing is conducted by placing connector pin contacts under a high potential voltage, and measuring the insulation resistance and monitoring for insulation resistance breakdown. However, Hipot testing will not identify malfunctioning of the connector's attenuation characteristics or capacitance values.
Manual bench tests may be performed on filter pin connectors to measure for continuity between corresponding pin contacts using a digital volt meter (DVM), and to verify proper capacitance range using a capacitance meter. However, bench tests of these types only serve as preliminary test procedures and provide only limited information with respect to the proper operation or type of malfunction of the filter pin connector under test. Additionally, such manual tests are very time-consuming to perform, particularly on a connector having numerous pin contacts to be tested.
A problem associated with filter pin connectors is that a failure in the connector's signal attenuation characteristics is very difficult to discover, both prior to and after installation into a system. Once the filter pin connector is installed in a system, a failure of the connector is virtually indistinguishable from other types of failures in the signal path. Military Standard 2120, MIL-STD-2120, Aug. 27, 1984, Section 5.2.6.1 discusses a manual test procedure for performing attenuation testing of a filter pin connector. The manual test requires RF probes to be connected between pin contacts on one side of the filter pin connector and a signal generator, and between pin contacts on the other side of the filter pin connector and a RF microvoltmeter. The probes and signal generator must be capable of operating in a frequency range between 10 Mhz and 1 Ghz. All of the equipment used for the test requires calibration before any measurements are taken. The test must be repeated for each pin contact of the filter pin connector under test, and the test equipment requires re-calibration between each test because movement of the test probes affects the response of the test equipment to the test signals provided by the signal generator, especially at high frequencies, i.e., 200 Mhz to 1 Ghz. Therefore, a manual attenuation test of this type is extremely time-consuming and costly, and may be highly susceptible to interference and noise resulting in high error values and potentially making the test results un-repeatable and inconclusive.